#!/usr/bin/bash
#
# script to update /etc/sysconfig/kdump to use the latest
# kernel package as the dump kernel
#
# optional argument --grub causes kdump kernel cmdline to
# be added to rt kernel grub entries
#

me=$(basename $0)
rpmcmd='rpm -q --last'

function fatal () {
    echo "$me: " $1
    exit -1
}

function usage () {
    echo "usage: $me [-g|--grub] [-r|--rhel] [-v|--verbose] [-h|--help]"
    echo "       --grub    - add crashkernel arg to rt grub entries"
    echo "       --rhel    - use the RHEL-8 kernel as the kdump kernel"
    echo "                   (the default is to use the RHEL-RT kernel)"
    echo "       --verbose - print out actions"
    echo "       --help    - print this message"
    exit -1
}

function report() {
    [ $verbose -eq 1 ] && echo $1
}

# return the latest package version of specified package name
function latest_package_ver() {
    local pkg=$1
    local ver=$($rpmcmd $pkg | head -1 | awk '{print $1}')

    if [ $? -ne 0 ]; then
	fatal "  error fetching version for $pkg"
    fi
    echo ${ver#$pkg-}
    return 0
}

# get the kernel version of hhe latest installed kernel
function vmlinux_ver() {
    local ver=$1
    local vmver=''
    for i in $(cd /boot; echo vmlinuz-*); do
	if [ "${i#vmlinuz-$ver}" != "$i" ]; then
	    vmver=${i#vmlinuz-}
	    echo $vmver
	    return 0
	fi
    done
    return 1
}

# find all the grub indexs for installed rhel-rt kernels
# returns a comma-separated list of indices for use
# by the grubby command
function find_rt_kernel_indexes_rhel_rt() {
    local awkscript='BEGIN{FS="="; ORS=","} $1 ~ /^index/{idx=$2;}
		$2 ~ /.rt.*.el8.x86_64/ &&
		$1 ~ /^kernel/ {print idx}'
    local rt_idx_list=$(/sbin/grubby --info=ALL | /usr/bin/awk "$awkscript")

    echo $rt_idx_list | sed -e 's/,$//'
    return 0
}

#############################################################################

# make sure we're root
if [ $(id -u) -ne 0 ]; then
    echo "  must be root to run $me!"
    usage
fi

# process options
dogrub=0
userhel=0
verbose=0
TEMP=$(getopt --options "grvh" --longoptions="grub,rhel,verbose,help" -- "$@")
if [ $? -ne 0 ]; then
    usage
fi
eval set -- "$TEMP"
while true; do
    case "$1" in
	-g|--grub)
	    dogrub=1
	    shift
	    ;;
	-r|--rhel)
	    userhel=1
	    shift
	    ;;
	-v|--verbose)
	    verbose=1
	    shift
	    ;;
	-h|--help)
	    usage
	    ;;
	--) shift ; break ;;
	*)
	    echo "internal error!"
	    usage
	    ;;
    esac
done

# warn if /etc/sysconfig/kdump does not exist
if [ ! -f /etc/sysconfig/kdump ]; then
    echo "  File /etc/sysconfig/kdump not found."
    echo "  Please, check your kexec-tools installation."
    exit 1
fi

if [ $dogrub = 0 ]; then
    echo "Not performing changes to /etc/grub.conf"
    echo
    # check if there is memory reserved for the kexec kernel
    if ! cat /proc/cmdline | grep -e crashkernel > /dev/null; then
        echo "  Kernel DOES NOT have memory reserved for kdump kernel..."
        echo "  Use --grub option to enable crashkernel option on kernel command line"
	echo
    fi
fi

# select the right kdump kernel
if [ $userhel -eq 1 ]; then
	KDUMP_KERNEL="kernel"
else
	KDUMP_KERNEL="kernel-rt"
fi
# get the version of the latest installed kernel
kver=$(latest_package_ver $KDUMP_KERNEL)
if [ -z "$kver" ]; then
    fatal "  Can't find $KDUMP_KERNEL package information!"
fi

report "  making kernel-$kver the kdump kernel"

# find the vmlinux version info for the latest kernel package
vmlinux_version=$(vmlinux_ver $kver)
if [ -z "$vmlinux_version" ]; then
    fatal "  Can't get vmlinux version!"
fi

# now edit the /etc/sysconfig/kdump file
sed -e "s/^KDUMP_KERNELVER.*$/KDUMP_KERNELVER=\"$vmlinux_version\"/" \
    /etc/sysconfig/kdump >/tmp/kdump.$$
mv /etc/sysconfig/kdump /etc/sysconfig/kdump.save && \
    mv /tmp/kdump.$$ /etc/sysconfig/kdump

# if requested, update the grub entries for the rt kernels
if [ $dogrub = 1 ]; then
    rtver=$(latest_package_ver kernel-rt)
    if [ -z "$rtver" ]; then
	fatal "  Can't find kernel-rt package information!"
    fi
    # RHEL-RT kernel
    kernels=$(find_rt_kernel_indexes_rhel_rt)
    if [ ! -z $kernels ]; then
        report "  adding 'crashkernel=auto' arg to grub entries: $kernels"
        /sbin/grubby --update-kernel=$kernels --args="crashkernel=auto"
    fi
fi

exit $?